The structures of poly(1,4-phenylenesulfone), [1,4-ArSO2](n) (Ar = 1,4-phenylene), and its tetrasulfone oligomer ArSO2ArSO2ArSO2ArSO2Ar (Ar = phenyl or 1,4-phenylene) have been determined from X-ray powder diffraction data interfaced to molecular simulation and diffraction modeling. An initial model for the tetrasulfone oligomer was developed using conformational and packing information obtained from a single-crystal X-ray determination of the structure of the trisulfone ArSO2ArSO2ArSO2Ar, in which the aromatic ring planes lie essentially orthogonal to a plane defined by the bridging C-S-C groups. Energy-minimization and crystallographic refinement of the tetrasulfone structure by Pawley and Rietveld methods yielded an agreement factor (R-wp) of 15.3%., and an analogous approach led to solution of the crystal structure of poly(1,4-phenylenesulfone) (R-wp = 5.5%). In all three structures, the diaryl sulfone units adopt near-perfect open-book conformations and the molecules crystallize with the aromatic rings of laterally adjacent chains essentially parallel. The polymer unit cell is C-centered orthorhombic (two chains per cell), space group Cmcm, with a = 10.79, b = 5.05, and c = 9.97 Angstrom. The polymer chain adopts 2(1) helical geometry, and crystal packing is dominated by S=O...H-C interactions (O...H = 2.68 Angstrom).